<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>菜单</title>
    <style>
        *{
            margin: 0px;
            padding: 0px;
            position: relative;
        }
        div{
            width: 50px;
            height: 200px;
            background-color: aqua;
            margin-top: 200px;
            position: absolute;
            left: -50px;
            opacity: 0.5;
            transition: left 1s;
        }
        button{
            width: 20px;
            height: 50px;
            margin-left: 50px;
            margin-top: 75px;
        }
        div:hover{
            left: 0px;
            opacity: 1;
        }
    </style>
</head>
<body>
    <div>
        <button>菜单</button>
    </div>
</body>
</html>